When specimens are observed with use of Transmission Electron Microscopes (Hereinafter referred to as TEM) or Scanning Transmission Electron Microscopes (Hereinafter referred to as STEM) the specimen holder is located inside the TEM or STEM. The holder is inserted into a goniometer stage (A goniometer stage is a device that may move in 4 directions allowing individual specimens to be observed in different positions, tilt angles and height) and selection between specimens may be done during observation at the position of the electron beam optical axis.
The detailed explanation follows here. Regarding the goniometer stage FIG. 1 is the mechanical drawing referred to hereinafter. The shadow area shows cross-sectional surface. The area of observation is limited, and the specimen holder (3) together with the specimen (1) is kept in place by item (8) of the goniometer stage. The location of the specimen itself (1) is at the center of the point of electron beam optical axis (center of 13, 14) inside the electron microscope column (15). For observation of various positions of a specimen (1) at the position of the optical axis (center of 13, 14) it is possible to move the specimen holder (3) along the two horizontal axes (13, 14). The items (21, 22, 23) allow the specimen holder (3) together with the specimen (1) to be moved along the horizontal axis (14) hereinafter referred to as X-axis direction. The items (18, 19, 20) allow the specimen holder (3) together with the specimen (1) to be moved along the horizontal axis (13) hereinafter referred to as Y-axis direction. It is also possible to move the specimen holder (3) together with the specimen. (1) in the vertical direction along the optical axis (center of 13, 14), hereinafter referred to as Z-axis direction. Furthermore it is possible to tilt the specimen holder (3) together with the specimen (1) to create an inclination, hereinafter referred to as Alpha angle, of the specimen (1) around the X-axis direction. This is achieved by rotating the complete goniometer stage.
Regarding the specimen holder (3), hereinafter the directions of it are hereby defined and referred to as front-end and rear-end. The front-end is defined as the position of the tip of the specimen holder near the electron beam optical axis (center of 13, 14). Rear-end is defined as the position of the handle (5) of the specimen holder (3).
Inserting a specimen holder (3) or similar into the TEM or STEM ultrahigh-vacuum pumped column area (12) requires pumping vacuum of the area around the specimen holder (3) itself. This is performed with a so-called airlock valve system. The airlock pumps vacuum around the area from front-end of specimen holder (3) until the location of the vacuum seal (16). After airlock pumping, the pumped area may be pressure-wise connected to the ultrahigh-vacuum pumped column area (12) by opening the airlock. The airlock pumping procedure usually takes from 1 to 3 minutes. Each time the airlock pumping procedure is performed the ultrahigh-vacuum pumped column area (12) vacuum level will deteriorate. Therefore it is not possible to sequentially retract and insert the holder during a short period of time.
The vacuum level inside the ultrahigh-vacuum pumped column area (12) will deteriorate each time a specimen (1) is replaced. The deterioration of the ultrahigh-vacuum pumped column area will cause contamination of specimens during observation with the electron beam. Hence it is an advantage to be able to fit several specimens to one single specimen holder (3) to reduce the number of specimen replacements.
The detailed explanation of the airlock valve system mentioned above is omitted since it is not an essential part of the invention itself. The location of the airlock valve system is the item number 4 of mechanical FIG. 1.
Existing technology allows several specimens to be mounted in one specimen holder. In such type of holders the specimens are mounted in a row and may slide along the X-axis direction (14). They also allow switching between specimens during observation with the TEM or STEM. Specimen holders that allow tilt of the specimen (1) to create an inclination, hereinafter referred to as Beta angle, of the specimen (1) around the Y-axis direction (13) also exist. A specimen holder allowing several specimens to be mounted and allowing inclination of the Beta angle is not known.
Existing technology allows several specimens to be loaded into one specimen holder before observation. The specimens are mounted along the X-axis direction (14) and may slide between specimens during observation. Further on, specimen holders that allow tilt of the Beta angle, which is inclination around the Y-axis direction (13), are currently available. However, specimen holders that allow the above described Beta tilt combined with technology allowing several specimens to be loaded in one specimen holder are currently not available.
The detailed explanation follows here. Regarding the TEM or STEM it uses a strong and highly stable magnetic field lens to achieve the desired function of the electron microscope optical system. The purpose is to achieve best possible resolution images without disturbance from mechanical vibration or disturbing the stability of the magnetic field; the specimen holder itself is here a critical part of the achievable resolution performance. Designing a specimen holder demands consideration of mechanical strength to avoid vibrations. It is also necessary to design a specimen holder with non-magnetic materials to avoid disturbance of the highly stable magnetic field in the magnetic lens. Further on the physical space is very limited. The front-end of the specimen holder is typically designed with a diameter of 6 mm and maximum allowed diameter is around 10 mm. However designing a specimen holder with a large diameter will limit the achievable movement, especially Alpha tilt inclination and Beta tilt inclination. Considering all the difficulties of the above it insinuates why until now a specimen holder able to perform Beta tilt combined with loading several specimens into one specimen holder is not currently available. It is very difficult to design a specimen holder that allows the described desired function without loosing performance.
In recent years, use of an aberration correction device (known as Cs Corrector) has increased. The Cs corrector is a device for correction of spherical aberration caused in a convex magnetic lens typically used in a TEM or STEM. The use of Cs corrector devices has improved the performance of TEM or STEM significantly. In some cases two Cs correctors may be included in one microscope. A thin film amorphous specimen (standard adjustment specimen) is used for adjusting the Cs corrector to optimum performance. A case of a too thick or a non-suitable specimen will not allow adjustment of this Cs corrector to the optimum level of performance. It is preferred to always have easy access to a suitable specimen for adjustment of the Cs corrector.
The detailed explanation follows here. Regarding adjustment of the aberration correction device, until now the procedure has been as follows. A thin film amorphous specimen (standard adjustment specimen) is inserted into the goniometer stage of the TEM or STEM. At this point in time adjustment of the Cs corrector device may be performed. After this adjustment is completed, the specimen holder is removed from the TEM or STEM. The specimen actually desired for observation is now placed in to the holder and next into the TEM or STEM, in some cases using another specimen holder. This operation takes time and cause deterioration of the vacuum level as described above.
In addition, the room temperature being different from the temperature inside the microscope column (12) influences the material of the specimen holder, causing an expansion or contraction of the same. It is further affected by the mechanical stress caused in the above-mentioned airlock (4) pumping procedure. This result in drift of the specimen (1) and it may last for a considerable time causing difficulties to achieve optimum resolution performance. The delay may vary due to temperature conditions but cases of half an hour or more of stabilization wait time can be considered common.
There are cases of observing specimens that needs to be orientated with use of Alpha inclination and Beta inclination. When observing crystalline specimens it is necessary to position the crystallographic orientation of the specimen itself along the electron beam optical axis. This is achieved by tilting the specimen holder (3) together with the specimen (1) to create an inclination of the specimen (1) around the X-axis direction and tilting the specimen holder (3) together with the specimen (1) to create an inclination of the specimen (1) around the Y-axis. After this crystallographic orientation has been adjusted it would be optimum to be able to switch to a thin film amorphous specimen (standard adjustment specimen) suitable for electron optics adjustments. A specimen holder covering these functions has not yet been available.
Therefore, it is an object of the present invention to provide a significantly beneficial specimen holder which allows mounting one or more specimens, for example, a specimen to be examined and a standard adjustment specimen for aberration correction in one specimen holder at the same time, thereby observing each specimens.